Both RMI and JMS cache coordination work with Oracle WebLogic. When a WebLogic cluster is used JNDI is replicated among the cluster servers, so an <tt>rmi.url</tt> or <tt>jms.host</tt> are not required. For JMS cache coordination the JMS topic should only be deployed to only one of the servers (as of Oracle WebLogic 10.3.6). It may be desirable to have a dedicated JMS server is the JMS messaging traffic is heavy.

+

+

Usage of other JMS services in WebLogic may have other requirements.

===Cache Coordination and Glassfish===

===Cache Coordination and Glassfish===

+

JMS cache coordination works with Glassfish. When a Glassfish cluster is used JNDI is replicated among the cluster servers, so a jms.host is not required.

+

+

Usage of other JMS services in Glassfish may have other requirements.

+

+

RMI cache coordination does not work when the JNDI naming service option is used in a Glassfish cluster (see [https://bugs.eclipse.org/bugs/show_bug.cgi?id=359395 bug#359395]). RMI will work if the <tt>"eclipselink.cache.coordination.naming-service"</tt> is set to <tt>rmi</tt>. Each server must provide its own <tt>"eclipselink.cache.coordination.rmi.url"</tt> option, either by having a different persistence.xml per server, or setting the url as a System property in the server, or through a customizer.

+

+

===Cache Coordination and IBM WebSphere===

+

JMS cache coordination may have issues on IBM WebSphere. Usage of a Message Driven Bean may be required to allow access the JMS. To use an MDB with cache coordination set the <tt>"eclipselink.cache.coordination.protocol"</tt> option to <tt>jms-publishing</tt>. The application will also have to deploy an MDB that processing cache coordination messages in its <tt>ear</tt>.

Clustering and Cache Coordination

An application cluster is a set of middle tier server machines or VMs servicing requests for a single application, or set of applications. Multiple servers are used to increase the scalability of the application and/or to provide fault tolerance and high availability. Typically the same application will be deployed to all of the servers in the cluster and application requests will be load balanced across the set of servers. The application cluster will access a single database, or a database cluster. An application cluster may allow new servers to be added to increase scalability, and for servers to be removed such as for updates and servicing.

EclipseLink can function in any clustered environment. The main issue in a clustered environment is utilizing a shared persistence unit (L2) cache. If you are using a shared cache (enabled by default in EclipseLink), then each server will maintain its own cache, and each caches data can get out of sync with the other servers and the database.

EclipseLink provides cache coordination in a clustered environment to ensure the servers caches are is sync.

There are also many other solutions to caching in a clustered environment, including:

Use optimistic locking to ensure write consistency (writes on stale data will fail, and will automatically invalidate the cache).

Use a distributed cache (such as Oracle TopLink Grid's integration of EclipseLink with Oracle Coherence).

Use database events to invalidate changed data in the cache (such as EclipseLink's support for Oracle DCN/QCN).

Cache coordination enables a set of persistence units deployed to different servers in the cluster (or on the same server) to synchronize their changes. Cache coordination works by each persistence unit on each server in the cluster being able to broadcast notification of transactional object changes to the other persistence units in the cluster. EclipseLink supports cache coordination over RMI and JMS. The cache coordination framework is also extensible so other options could be developed.

Cache coordination works by broadcasting changes for each transaction to the other servers in the cluster. Each other server will receive the change notification, and either invalidate the changed objects in their cache, or update the cached objects state with the changes. Cache coordination occurs after the database commit, so only committed changes are broadcast.

Cache coordination greatly reduces to chance of an application getting stale data, but does not eliminate the possibility. Optimistic locking should still be used to ensure data integrity. Even in a single server application stale data is still possible within a persistence context unless pessimistic locking is used. Optimistic (or pessimistic) locking is always required to ensure data integrity in any multi-user system.

Configuring Cache Coordination

Cache coordination is configured using persistence unit properties. The following cache coordination properties are supported:

Cache Coordination Persistence Unit Properties

Property

Description

Default

Required?

eclipselink.cache.coordination.protocol

Enable cache coordination using the communication protocol:

rmi - Use Java RMI to broadcast changes.

rmi-iiop - Use Java RMI over CORBA IIOP to broadcast changes.

jms - Use the Java Messaging Service to broadcast changes.

jms-publishing - Allows an EJB MessageDrivenBean to be used to broadcast changes. The MDB must be configured separately.

<class-name> - The fully qualified class name of a custom implementation of a TransportManager.

no coordination

Required

eclipselink.cache.coordination.channel

Sets the channel for cache coordination. All persistence units using the same channel will be coordinated.

EclipseLinkCommandChannel

Optional

eclipselink.cache.coordination.propagate-asynchronously

Configures if changes are broadcast using a separate thread. If set to false the transaction will wait for all servers to be notified before returning.

Note that JMS is always asynchronous.

true

Optional

eclipselink.cache.coordination.thread.pool.size

Configures thread pool size for cache coordination threads.

RMI cache coordination will spawn one thread per node to send change notifications. RMI also spawns a thread to listen for new node notifications.
JMS cache coordination will spawn one thread to receive JMS change notification messages (unless an MDB is used). JMS also spawns a thread to process the change notification (unless an MDB is used).
A size of 0 indicates no thread pool should be used, and threads will be spawned when required.

32

Optional

eclipselink.cache.coordination.remove-connection-on-error

Set if a connection should be removed if a communication error occurs when coordinating with it.

This is normally used for RMI coordination in case a server goes down (it will reconnect when it comes back up).

true

Optional

eclipselink.cache.coordination.naming-service

Set the naming service to use to look-up and register the RMI cache coordination service, either:

jndi - The server's Java Naming and Directory Interface is used. If the server's JNDI is replicated in an application server cluster, then the rmi.url option is not required.

rmi - The RMI registry is used. This can be used if JNDI is not available, or the JNDI implementation does not support RMI objects.

jndi

Optional

eclipselink.cache.coordination.jndi.user

Set the application server user name to connect to JNDI with. This is only required if JNDI requires authentication.

no authentication

Optional

eclipselink.cache.coordination.jndi.password

Set the application server user password to connect to JNDI with. This is only required if JNDI requires authentication.

This is normally not required if connecting to a local service.

no authentication

Optional

eclipselink.cache.coordination.rmi.url

Only required by RMI cache coordination. Sets the URL of the host server. This is the URL that other cluster members should use to connect to this host. This may not be required in a clustered environment where JNDI is replicated. This can also be set as a System property or using a SessionCustomizer to avoid a separate persistence.xml per server.

local

Optional

eclipselink.cache.coordination.rmi.multicast-group

Only used for RMI coordination. Sets the multicast socket group address. The multicast group is used to find other members of the cluster.

239.192.0.0

Optional

eclipselink.cache.coordination.rmi.multicast-group.port

Only used for RMI coordination. Sets the multicast socket group port. The multicast group is used to find other members of the cluster.

3121

Optional

eclipselink.cache.coordination.rmi.announcement-delay

Only used for RMI coordination. Sets the number of milliseconds to wait for announcements from other cluster members on start-up.

1000

Optional

eclipselink.cache.coordination.rmi.packet-time-to-live

Only used for RMI coordination. Sets the multicast socket packet time to live. The multicast group is used to find other members of the cluster. Set the number of hops the data packets of the session announcement will take before expiring. The default is 2, a hub and an interface card to prevent the data packets from leaving the local network.

Note that if sessions are hosted on different LANs that are part of WAN, the announcement sending by one session may not reach other sessions. In this case, consult your network administrator for the right time-to-live value or test your network by increase the value until sessions receive announcement sent by others.

2

Optional

eclipselink.cache.coordination.jms.topic

Only used for JMS coordination. Sets the JMS topic name.

All persistence units sharing the same JMS topic from the same JMS service will be coordinated.

Cache Coordination and Oracle WebLogic

Both RMI and JMS cache coordination work with Oracle WebLogic. When a WebLogic cluster is used JNDI is replicated among the cluster servers, so an rmi.url or jms.host are not required. For JMS cache coordination the JMS topic should only be deployed to only one of the servers (as of Oracle WebLogic 10.3.6). It may be desirable to have a dedicated JMS server is the JMS messaging traffic is heavy.

Usage of other JMS services in WebLogic may have other requirements.

Cache Coordination and Glassfish

JMS cache coordination works with Glassfish. When a Glassfish cluster is used JNDI is replicated among the cluster servers, so a jms.host is not required.

Usage of other JMS services in Glassfish may have other requirements.

RMI cache coordination does not work when the JNDI naming service option is used in a Glassfish cluster (see bug#359395). RMI will work if the "eclipselink.cache.coordination.naming-service" is set to rmi. Each server must provide its own "eclipselink.cache.coordination.rmi.url" option, either by having a different persistence.xml per server, or setting the url as a System property in the server, or through a customizer.

Cache Coordination and IBM WebSphere

JMS cache coordination may have issues on IBM WebSphere. Usage of a Message Driven Bean may be required to allow access the JMS. To use an MDB with cache coordination set the "eclipselink.cache.coordination.protocol" option to jms-publishing. The application will also have to deploy an MDB that processing cache coordination messages in its ear.